I've owned a few of their horse products (the back pad initially, followed by the full sheet, a set of polos, and a set of standing bandages).
The back pad I was never able to really use - it's an awkward size and shape and even after I had a blanket modified to fit it...it wasn't helpful. I wound up getting the sheet for Tristan. I never noticed a huge difference with it, but he's a horse with such a multitude of health issues, none of which have ever been muscular or even really joint related, so I'm not sure I would have.
The standing bandages I got when he was recovering from a pulled suspensory, and he ate them in less than 10 minutes. I managed to not kill him.
I do know that the amazing massage/body work guy who works on the horses in the barn was really impressed by the products despite a lot of initial skepticism. He's somebody I'd absolutely trust in such matters. Quite a few of the horses in the barn practically live in their BoT sheets and the rider swears it helps them - she's also sponsored by them, so has reason to say that
A friend of mine who has a lot of arthritis in her hands has the gloves and sleeps in them. She swears by them. If she takes them off during the night and doesn't put them back on, she says she can't make a fist in the morning. Wearing the gloves overnight, she can.
I see a lot of them at agility trials, and people again claim to notice a difference in their dogs.
My take on them is that I'd absolutely get one of the sheets for my dogs if they were having any muscle or joint issues. It is non-invasive, and certainly isn't going to hurt.